/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.solr.search;

import org.apache.lucene.search.*;

/**
 * Extra lucene sorting utilities & convenience methods
 * 
 * 
 * 
 */

public class Sorting {

	/**
	 * Returns a {@link SortField} for a string field. If nullLast and nullFirst
	 * are both false, then default lucene string sorting is used where null
	 * strings sort first in an ascending sort, and last in a descending sort.
	 * 
	 * @param fieldName
	 *            the name of the field to sort on
	 * @param reverse
	 *            true for a reverse (desc) sort
	 * @param nullLast
	 *            true if null should come last, regardless of sort order
	 * @param nullFirst
	 *            true if null should come first, regardless of sort order
	 * @return SortField
	 */
	public static SortField getStringSortField(String fieldName,
			boolean reverse, boolean nullLast, boolean nullFirst) {
		if (nullLast) {
			if (!reverse)
				return new SortField(fieldName, nullStringLastComparatorSource);
			else
				return new SortField(fieldName, SortField.Type.STRING, true);
		} else if (nullFirst) {
			if (reverse)
				return new SortField(fieldName, nullStringLastComparatorSource,
						true);
			else
				return new SortField(fieldName, SortField.Type.STRING, false);
		} else {
			return new SortField(fieldName, SortField.Type.STRING, reverse);
		}
	}

	static final FieldComparatorSource nullStringLastComparatorSource = new MissingStringLastComparatorSource(
			null);
}
